Phase-change random access memory device and method of manufacturing the same

ABSTRACT

Provided are a Phase-change Random Access Memory (PRAM) device and a method of manufacturing the same. In particular, a PRAM device including a heating layer, wherein the heating layer comprises first and second heating layers having different physical properties from each other and a method of manufacturing the same are provided. Since the PRAM device according to the present invention includes a heating layer having optimal heating characteristics, a PRAM device having high reliability and excellent operating characteristics can be manufactured.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2006-0122618, filed on Dec. 5, 2006, and 10-2007-0043800, filed onMay 4, 2007 in the Korean Intellectual Property Office, the disclosureof which are incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Phase-change Random Access Memory(PRAM) device and a method of manufacturing the same, and moreparticularly, to a PRAM device having high reliability and excellentoperating characteristics by including a heating layer having optimalheating characteristics and a method of manufacturing the same. Thiswork was supported by the IT R&D program of MIC/IITA. [2005-S-072-02,Technology of a nano scale phase change data storage]

2. Description of the Related Art

Phase-change Random Access Memory (PRAM) devices are memory devicesusing a characteristic that electrical resistance of a phase changematerial formed of a chalcogenide compound including the elements Se,Te, and S is changed according to its crystalline phase. That is, thecrystalline phase of the phase change material can be reversiblyswitched between a crystalline state and an amorphous state according toa voltage or current applied to the phase change material, each statehaving a different electrical resistance. Such PRAM devices arenon-volatile, fast, and can be highly integrated.

Since electrical resistance of a phase change material is significantlychanged according to whether the phase change material is in acrystalline or an amorphous state, physical properties of the phasechange material can be used to apply the phase change material for useas information storing devices. More specifically, a PRAM memory deviceis operated according to a set process and a reset process describedbelow. The set process comprises changing a phase change material layerof the PRAM memory device from an amorphous state with high resistanceto a crystalline state with low resistance. The reset process compriseschanging the phase change material layer of the PRAM memory device froma crystalline state to an amorphous state. For the set and resetprocesses, two types of current pulses having different amplitudes andtimes are needed. A reset pulse having a high amplitude and short timeincreases the internal temperature of a phase change material layerabove a melting point so that a crystalline structure of the phasechange material layer is maintained in a liquid state, and is cooleddown after the pulse is completed, so that the crystalline structure ofthe phase change material layer is changed into an amorphous state. Aset pulse having a relatively lower amplitude and longer time than thereset pulse increases temperature of the phase change material layerabove a crystallization temperature so that a crystalline structure ofthe phase change material layer is changed into a crystalline state.

FIGS. 1A and 1B are side cross-sectional views of a conventional PRAMdevice. Referring to FIG. 1A, the conventional PRAM device includes alower electrode 10 and an upper electrode 50 respectively disposed onthe lower part and the upper part of a phase change material layer 40and a heating layer 20 disposed to contact the phase change materiallayer 40. Also, portions of each of the phase change material layer 40and the heating layer 20 required to be insulated from each other areinsulated by an interlayer insulation film 30. Such structure mayselectively have a structure where a heating layer 22 having a smallcross section is disposed below a phase change material layer 42, asillustrated in FIG. 1B. Here, a lower electrode 12, an upper electrode52, and an interlayer insulation film 32 may correspond to the lowerelectrode 10, the upper electrode 50, and the interlayer insulation film30 illustrated in FIG. 1A, respectively.

An operation of the conventional PRAM device is described below withreference to FIGS. 1A and 1B.

When a current is applied through the lower electrodes 10 and 12 and theupper electrodes 50 and 52, joule heat is generated from the heatinglayers 20 and 22 and phases of some regions of the phase change materiallayers 40 and 42 are changed. Since heat generated from the phase changematerial layers 40 and 42 may not be sufficient to cause phase change,the heating layers 20 and 22 are employed in this regard. Accordingly,in general, the heating layers 20 and 22 may be formed of materialshaving high electrical resistance which can generate a sufficient amountof heat.

TiN, TiAlN, and TiSiC are widely used as the materials for the heatinglayers 20 and 22, and W can also be used as a material for the heatinglayers 20 and 22. For these materials to be used as the heating layers20 and 22, they should have high electrical resistivity (ρ), low thermalconductivity, and low specific heat. The electrical resistivity shouldbe high to generate a large amount of heat, thermal conductivity shouldbe low to reduce unnecessary heat loss to the outside, and specific heatshould be low to cause large temperature changes. The most importantparameters of these properties are electrical resistivity and thermalconductivity.

Conventionally, such heating layers 20 and 22 are formed of a singlematerial. However, materials that satisfy the above conditions have notyet been found. Accordingly, heating layers using excellent physicalproperties of conventionally known materials are required.

SUMMARY OF THE INVENTION

The present invention provides a memory device having high reliabilityand excellent operating characteristics by including a heating layerhaving optimal heating characteristics.

The present invention also provides a method of manufacturing a memorydevice having high reliability and excellent operating characteristicsby including a heating layer having optimal heating characteristics.

According to an aspect of the present invention, there is provided aPhase-change Random Access Memory (PRAM) device including: an lowerelectrode formed on a semiconductor substrate; an upper electrode formedon the lower electrode; a phase change material layer disposed betweenthe lower electrode and the upper electrode, and a heating layerdisposed between the upper electrode or the lower electrode and thephase change material layer, wherein the heating layer comprises a firstheating layer and a second heating layer, the first heating layercontacting the phase change material layer and the second heating layercontacting the first heating layer and being disposed between the firstheating layer and the upper electrode or the lower electrode.

The first heating layer may include a material having lower resistivitythan the resistivity of a material forming the second heating layer.More specifically, the first heating layer may include titanium nitride(TiN) and the second heating layer comprises polysilicon (poly Si) orpolysilicon germanium (poly-SiGe).

The first heating layer may include a material which blocks diffusion oftitanium. More specifically, the first heating layer may include atleast one selected from the group consisting of TaN, TiAlN, WN, WBN,TiSiN, TaSiN, WSiN, TiSiC, TaSiC, WSiC, and low resistivity TiN. Inparticular, the second heating layer may include high resistivity TiN.The low resistivity TiN may have a resistivity of 100 μΩ·cm or less.

The first heating layer may include a material having higher resistivitythan the resistivity of a material forming the second heating layer andthe second heating layer comprises a material having lower thermalconductivity than the thermal conductivity of a material forming thefirst heating layer. More specifically, the first heating layer mayinclude TiAlN and the second heating layer comprises TaN, TiN, orpolysilicon germanium (poly-SiGe).

According to another aspect of the present invention, there is provideda method of manufacturing a Phase-change Random Access Memory (PRAM)device including: forming a heating material layer comprising a firstheating material layer and a second heating material layer on asubstrate including a lower electrode; etching the heating materiallayer to form a heating layer comprising a first heating layer and asecond heating layer; forming an insulation layer on the top and sidesurfaces of the heating layer and on the top surface of the lowerelectrode; forming a contact hole in the insulation layer so that aportion of the heating layer is exposed; forming a phase-change materiallayer filling the contact hole; and forming an upper electrode on thephase-change material layer.

According to another aspect of the present invention, there is provideda method of manufacturing a Phase-change Random Access Memory (PRAM)device including: forming an insulation layer on a substrate including alower electrode; forming a contact hole in the insulation layer so thata portion of the lower electrode is exposed; forming a second heatinglayer in the contact hole; forming a first heating layer on the secondheating layer; and sequentially forming a phase-change material layerand an upper electrode on the first heating layer.

The first heating layer may include a material having lower resistivitythan the resistivity of a material forming the second heating layer. Thefirst heating layer may include titanium nitride (TiN) and the secondheating layer comprises polysilicon (poly Si) or polysilicon germanium(poly-SiGe).

The first heating layer may include a material which blocks diffusion oftitanium. More specifically, the first heating layer may include atleast one selected from the group consisting of TaN, TiAlN, WN, WBN,TiSiN, TaSiN, WSiN, TiSiC, TaSiC, WSiC, and low resistivity TiN. Thesecond heating layer may include high resistivity TiN. The lowresistivity TiN may have resistivity of 100 μΩ·cm or less.

The first heating layer may include a material having higher resistivitythan the resistivity of a material forming the second heating layer andthe second heating layer comprises a material having lower thermalconductivity than the thermal conductivity of a material forming thefirst heating layer. More specifically, the first heating layer mayinclude TiAlN and the second heating layer comprises TaN, TiN, orpolysilicon germanium (poly-SiGe).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIGS. 1A and 1B are side cross-sectional views of a conventionalPhase-change Random Access Memory (PRAM) device;

FIGS. 2A and 2B are side cross-sectional views of PRAM devices accordingto embodiments of the present invention;

FIG. 3 is a graph showing a small reset current when polysilicongermanium (poly-SiGe) is used as a material for forming a heating layer.

FIG. 4 is a graph showing a reset failure when poly-SiGe is used as amaterial for forming a heating layer;

FIG. 5 is a graph for describing an operation performed with respect toa heating layer including poly-SiGe, wherein the operation does notresult in a reset failure since the heating layer is formed of a duallayer;

FIGS. 6A and 6B are concentration profile graphs showing diffusion oftitanium according to repeated operation of a device when highresistivity TiN is used to form a heating layer;

FIGS. 7A through 7C are side cross-sectional views sequentiallyillustrating a method of manufacturing a PRAM device, according to anembodiment of the present invention;

FIGS. 8A through 8C are side cross-sectional views sequentiallyillustrating a method of manufacturing a PRAM device, according toanother embodiment of the present invention; and

FIG. 8D is a side cross-sectional view illustrating a selective methodof manufacturing a PRAM device, according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The invention may, however, be embodied inmany different forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art. In thedrawings, like reference numerals denote like elements. Furthermore,various elements and regions are schematically illustrated. Therefore,the present invention is not limited to sizes and distances illustratedin the accompanying drawings.

The present invention provides a Phase-change Random Access Memory(PRAM) device including a lower electrode formed on a semiconductorsubstrate, an upper electrode formed on the lower electrode, and a phasechange material layer disposed between the lower electrode and the upperelectrode, and more particularly, to a PRAM device further including aheating layer disposed between the upper electrode or the lowerelectrode and the phase change material layer, the heating layerincluding a first heating layer contacting the phase change materiallayer and a second heating layer contacting the first heating layer andbeing disposed between the first heating layer and the upper electrodeor the lower electrode.

FIGS. 2A and 2B are side cross-sectional views of PRAM devices 100 and200 according to embodiments of the present invention.

Referring to FIGS. 2A and 2B, the PRAM devices 100 and 200 according tothe current embodiments of the present invention include heating layers120 and 220 including first heating layers 121 and 221 and secondheating layers 122 and 222, lower electrodes 110 and 210, upperelectrodes 150 and 250, phase change material layers 140 and 240, andinterlayer insulation films 130 and 230, respectively, and are differentfrom the conventional PRAM device illustrated in FIG. 1A in that heatinglayers 120 and 220 illustrated in FIGS. 2A and 2B are formed of duallayers including first heating layers 121 and 221 and second heatinglayers 122 and 222 having different physical properties from each other,respectively.

It is obvious to one of ordinary skill in the art that the heatinglayers 120 and 220 are distinguished from the lower electrodes 110 and210 and are different from a metal wiring.

The lower electrodes 110 and 210, the upper electrodes 150 and 250, thephase change material layers 140 and 240, and the interlayer insulationfilms 130 and 230 may be formed of conventionally known materials andare not particularly limited.

The first heating layers 121 and 221 and the second heating layers 122and 222 can be formed of materials described in examples below accordingto required purposes.

EXAMPLE 1

In general, one of the desirable characteristics of the heating layer ofa PRAM device is high resistivity. If the resistivity is high, a largeamount of joule heat is generated so that a reset current required for areset operation is decreased and thus the power required to operate thePRAM device is also decreased. For example, polysilicon (poly Si) orpolysilicon germanium (poly-SiGe) has resistivity that is no less thantwice as high as that of TiN so that reset current can be significantlyreduced. FIG. 3 is a graph showing a small reset current whenpolysilicon germanium (poly-SiGe) is used as a material for forming aheating layer. Referring to FIG. 3, resistivity of poly-SiGe issignificantly higher than high resistivity (ρ) TiN.

However, when poly-SiGe is used alone as the heating layer, excessivejoule heat is generated due to high resistivity and thus a reset failurecan be generated. FIG. 4 is a graph showing a reset failure whenpoly-SiGe is used as a material for forming a heating layer. Referringto FIG. 4, when a programming current is applied to the heating layer ofa PRAM device in a first cycle, the crystalline structure of a phasechange material layer of the PRAM device is changed from a crystallinestate to an amorphous state (reset). Then, when a program current isagain applied to the heating layer of the PRAM device in a second cycle,the crystalline structure of the phase change material layer ismaintained in an amorphous state as illustrated in FIG. 4, instead ofchanging from an amorphous state to a crystalline state and as a result,the phase change material layer may be maintained in a state with highresistance (reset failure).

Such a reset failure can be prevented by forming the heating layer ofthe PRAM device as a dual layer. That is, referring to the PRAM devices100 and 200 of FIGS. 2A and 2B according to the current embodiments ofthe present invention, materials of the first heating layers 121 and 221and the second heating layers 122 and 222 differ from each other so asto prevent reset failures. In this regard, the second heating layers 122and 222 may be formed of high resistivity poly Si or poly-SiGe and thefirst heating layers 121 and 221 may be formed of a material withrelatively lower resistivity, for example, TiN. TiN may be highresistivity TiN having a resistivity greater than 100 μΩ·cm or lowresistivity TiN having a resistivity of 100 μΩ·cm or less.

FIG. 5 is a graph for describing an operation performed with respect toa heating layer including poly-SiGe, wherein the operation does notresult in a reset failure since the heating layer is formed of a duallayer.

In FIG. 5, the result of an experiment performed when the first heatinglayers 121 and 221 are formed of low resistivity TiN and the secondheating layers 122 and 222 are formed of poly-SiGe is illustrated.Referring to FIG. 5, the heating layers 120 and 220 are formed of a duallayer in the PRAM devices 100 and 200 according to the currentembodiments of the present invention and as a result, the phase changematerial layers 140 and 240 are reset in the first cycle and arenormally set in the second cycle and if program current is continuouslyincreased, the phase change material layers 140 and 240 are again reset.

According to the result of FIG. 5, the reset current of a PRAM deviceaccording to the present invention is twice that of a PRAM device usingonly poly-SiGe (refer to FIG. 4), however, is ⅕ the reset current of aPRAM device using high resistivity TiN (refer to FIG. 3).

A principle that reset failures are prevented by forming the PRAM deviceas illustrated in FIGS. 2A and 2B is not clearly defined. However, it ispresumed that a material such as TiN partly delays transfer of excessiveheat generated from a layer with high resistivity such as a poly Silayer or a poly-SiGe layer.

EXAMPLE 2

A single TiN layer is widely used for a conventional heating layer. Inparticular, high resistivity TiN is used. As illustrated in FIG. 3, whena heating layer is formed of low resistivity TiN, a phase changematerial layer is not reset and thus low resistivity TiN is not suitableas a material for forming a single heating layer.

Accordingly, in order to increase resistivity, a TiN heating layer isdeposited at a relatively low temperature or is controlled to havehigher composition in nitrogen concentration than that a stoichiometriccomposition by injecting nitrogen into a TiN thin film. However, such aTiN heating layer with high resistivity of 100 μΩ·cm or greater is notthermodynamically stable so that when the TiN heating layer contactsother materials, the TiN heating layer easily reacts.

FIGS. 6A and 6B are concentration profile graphs showing diffusion oftitanium according to repeated operation of a device when highresistivity TiN is used as a material for forming a heating layer. InFIGS. 6A and 6B, concentration of each element is illustrated accordingto depths. In particular, FIG. 6A illustrates concentration profiles ofelements immediately after the manufacture of a PRAM device and FIG. 6Billustrates concentration profiles of elements after repetitive cyclesof an operation of the PRAM device. Referring to FIGS. 6A and 6B, sincean operation of the PRAM device is repeatedly performed, a significantamount of titanium is diffused into a GeSbTe (GST) layer. In general, itis well known that titanium and tellurium are combined to form acomposition. Therefore, since such diffusion of titanium occurscontinuously, composition of the GST layer is changed so thatphase-change may not occur any more.

Accordingly, since the second heating layers 122 and 222 areconventional heating layers formed of high resistivity TiN and the firstheating layers 121 and 221 are formed of materials which can blockdiffusion of titanium, reliability of the PRAM devices 100 and 200 canbe significantly improved.

Materials which can block diffusion of titanium may include TaN, TiAlN,WN, WBN, TiSiN, TaSiN, WSIN, TiSiC, TaSiC, WSIC, and TiN, for example,low resistivity TiN, but are not limited thereto. In particular, lowresistivity TiN may have resistivity of 100 μΩ·cm or less, for example,20-100 100 μΩ·cm.

EXAMPLE 3

Table 1 below shows electrical resistivity, thermal conductivity, andspecific heat of a number of materials which can be used as the heatinglayer of the present invention, compared with a phase change material,Ge₂Sb₂Te₅.

TABLE 1 Specific Electric Resistivity Thermal Conductivity Heat (μΩ ·cm) (W/m · K) (J/cm³ · K) Ge₂Sb₂Te₅ 400 0.28 1.2 (crystalline) TiN 10015 3.25 TiAlN 400 30 0.7 TaN 200 8.8 2.9 poly Si >1000 31 1.63poly-SiGe >1000 4.7 1.85

As described above, the heating layer may have high electricalresistivity (ρ), low thermal conductivity, and a low specific heat.However, materials that satisfy such conditions hardly exist.

Meanwhile, as in the PRAM device of the present invention, when theheating layer is separated into two layers including a first heatinglayer and a second heating layer, physical properties that are moredesirable and preferable exist in each of the first and second heatinglayers.

More specifically, the first heating layers 121 and 221 contacts thephase change material layers 140 and 240 and transfers heat, so thatmaterials with high resistivity and small specific heat may bepreferable. Resistivity should be high so as to generate a large amountof heat and specific heat should be small to maximize a temperatureincrease. Also, the second heating layers 122 and 222 may be formed of amaterial with low thermal conductivity so as not to lose heat generatedfrom the first heating layers 121 and 221 to the lower electrodes 110and 210 or a metal wiring disposed below the second heating layers 122and 222.

Accordingly, TiAlN can be used as a material for forming the firstheating layer and TaN, TiN, or poly-SiGe can be used as a material forforming the second heating layer. That is, TiAlN has resistivity of 400μΩ·cm and specific heat of 0.7 J/cm³·K and is more preferable for thematerial of the first heating layer than any other material illustratedin Table 1. Also, TaN has thermal conductivity of 8.8 W/m·K and is morepreferable for the material of the second heating layer than any othermaterials (except poly SiGe) illustrated in Table 1.

Poly Si and poly-SiGe have higher resistivity than other materialslisted in Table 1. However, when poly Si and poly-SiGe are used asmaterials for forming the first heating layer, a reset failure may occuras illustrated in Example 1 with reference to FIG. 4 so that poly Si andpoly-SiGe may not be used as the first heating layer.

Hereinafter, a method of manufacturing a PRAM device according to anembodiment of the present invention is described.

FIGS. 7A through 7C are side cross-sectional views sequentiallyillustrating a method of manufacturing a PRAM device, according to anembodiment of the present invention.

Referring to FIG. 7A, a heating layer 320 including a first heatinglayer 321 and a second heating layer 322 may be formed on a lowerelectrode 310 by forming a first heating material layer (not shown) anda second heating material layer (not shown) formed thereon and etchingthe first heating material layer and the second heating material layerto form the first heating layer 321 and the second heating layer 322,respectively. A method of forming the first heating material layer andthe second heating material layer is not particularly restricted and canbe any method for forming a thin film. The lower electrode 310 may be,for example, formed as a metal wiring.

Then, the first heating material layer and the second heating materiallayer are appropriately etched to complete manufacture of the heatinglayer 320 including the first heating layer 321 and the second heatinglayer 322. The etching method can comprise at least one of wet etchingand dry etching that are well known in the art.

The first heating layer 321 and the second heating layer 322 can beformed using a combination of materials described above.

Alternatively, resistivity of materials forming the first heating layer321 can be lower than that of materials forming the second heating layer322. For example, the first heating layer 321 can be formed of TiN andthe second heating layer 322 can be formed of poly Si and poly-SiGe. Inparticular, the TiN may be high resistivity TiN having a resistivitygreater than 100 μΩ·cm or low resistivity TiN having a resistivity of100 μΩ·cm or less.

Alternatively, the first heating layer 321 can be selectively formed ofa material which can block diffusion of titanium. Alternatively, thesecond heating layer 322 can comprise a conventional heating layerincluding TiN. Materials which can block diffusion of titanium mayinclude TaN, TiAlN, WN, WBN, TiSiN, TaSiN, WSiN, TiSiC, TaSiC, WSiC, andTiN, for example, low resistivity TiN. However, the present invention isnot limited thereto.

Alternatively, resistivity of the material forming the first heatinglayer 321 may be higher than that of the material forming the secondheating layer 322 and thermal conductivity of the material forming thesecond heating layer 322 may be lower than that of the material formingthe first heating layer 321. For example, TiAlN can be used as amaterial for forming the first heating layer 321 and TaN, TiN, orpoly-SiGe can be used as a material for forming the second heating layer322.

Referring to FIG. 7B, an insulation layer 330 is formed to cover uppersurfaces of the heating layer 320 and the lower electrode 310 and then acontact hole 332 is formed in the insulation layer 330 so that a portionof the heating layer 320 is exposed. Referring to FIG. 7C, a phasechange material layer 340 is formed to fill the contact hole 332. Thephase change material layer 340 can be formed of any conventional phasechange material. A method of forming the phase change material layer 340to fill the contact hole 332 can be any method that is well known in theart and may be a sputtering method, a chemical vapor deposition (CVD)method having an excellent step coverage characteristic, or an atomiclayer deposition (ALD) method.

The phase change material layer 340 can also be formed to cover an upperportion of the insulation layer 330.

Then, an upper electrode 350 is formed on the phase change materiallayer 340. A method of forming the upper electrode 350 can be any methodthat is well known in the art and is not particularly restricted. Theupper electrode 350 and the phase change material layer 340 can beselectively etched so that some portions of the upper electrode 350 andthe phase change material layer 340 are remained on the insulation layer330.

FIGS. 8A through 8C are side cross-sectional views sequentiallyillustrating a method of manufacturing a PRAM device, according toanother embodiment of the present invention. The PRAM devicemanufactured using the method illustrated in FIGS. 8A through 8C isdifferent from the PRAM device manufactured using the method illustratedin FIGS. 7A through 7C. In particular, the difference is that a heatinglayer with a small cross-section that is surrounded by an insulationlayer is disposed beneath the lower part of a phase-change materiallayer in FIGS. 8A through 8C.

Referring to FIG. 8A, an insulation layer 430 is formed on a lowerelectrode 410 and then a contact hole 432 is formed in the insulationlayer 430 so that a portion of the lower electrode 410 is exposed. Thelower electrode 410 may be formed on a substrate (not shown). Then,referring to FIG. 8B, a second heating layer 422 is formed in thecontact hole 432. A method of forming the second heating layer 422includes depositing a material for forming the second heating layer 422in the contact hole 432 and performing a chemical mechanical polishing(CMP) method so that the upper surface of the second heating layer 422and the upper surface of the insulation layer 430 can be located on thesame plane.

Referring to FIG. 8C, a first heating layer 421 is formed on the secondheating layer 422 and a phase-change material layer 440 and an upperelectrode 450 are sequentially formed on the first heating layer 421.Alternatively, the first heating layer 421, the phase-change materiallayer 440, and the upper electrode 450 can be etched to be self-aligned.

Alternatively, a method of forming the first heating layer 421 may beselectively performed as illustrated in FIG. 8D. Referring to FIG. 8D,the first heating layer 421 is formed on the second heating layer 422and then the first heating layer 421 is etched to have a smallcross-section. Then, the phase-change material layer 440 and the upperelectrode 450 are formed and may be etched to be self-aligned asdescribed above.

In the embodiments illustrated in FIGS. 8A through 8D, the combinationof the materials used to form the first heating layer 421 and the secondheating layer 422 can be same as that of the embodiment illustrated inFIGS. 7A through 7C.

A PRAM device according to the present invention can be used in, forexample, mobile communication means such as computers and mobile phones,PDAs, electronic dictionaries, MP3 players, and other electronicdevices.

As described above, since the PRAM device according to the presentinvention includes a heating layer having optimal heatingcharacteristics, a PRAM device having high reliability and excellentoperating characteristics can be manufactured.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A Phase-change Random Access Memory (PRAM) device comprising: anlower electrode formed on a semiconductor substrate; an upper electrodeformed on the lower electrode; a phase change material layer disposedbetween the lower electrode and the upper electrode, and a heating layerdisposed between the upper electrode or the lower electrode and thephase change material layer, wherein the heating layer comprises a firstheating layer and a second heating layer, the first heating layercontacting the phase change material layer and the second heating layercontacting the first heating layer and being disposed between the firstheating layer and the upper electrode or the lower electrode.
 2. Thedevice of claim 1, wherein the first heating layer comprises a materialhaving lower resistivity than the resistivity of a material forming thesecond heating layer.
 3. The device of claim 2, wherein the firstheating layer comprises titanium nitride (TiN) and the second heatinglayer comprises polysilicon (poly Si) or polysilicon germanium(poly-SiGe).
 4. The device of claim 1, wherein the first heating layercomprises a material which blocks diffusion of titanium.
 5. The deviceof claim 4, wherein the first heating layer comprises at least oneselected from the group consisting of TaN, TiAlN, WN, WBN, TiSiN, TaSiN,WSiN, TiSiC, TaSiC, WSiC, and low resistivity TiN.
 6. The device ofclaim 5, wherein the second heating layer comprises high resistivityTiN.
 7. The device of claim 5, wherein the low resistivity TiN has aresistivity of 100 μΩ·cm or less.
 8. The device of claim 1, wherein thefirst heating layer comprises a material having higher resistivity thanthe resistivity of a material forming the second heating layer and thesecond heating layer comprises a material having lower thermalconductivity than the thermal conductivity of a material forming thefirst heating layer.
 9. The device of claim 8, wherein the first heatinglayer comprises TiAlN and the second heating layer comprises TaN, TiN,or polysilicon germanium (poly-SiGe).
 10. A method of manufacturing aPhase-change Random Access Memory (PRAM) device comprising: forming aheating material layer comprising a first heating material layer and asecond heating material layer on a substrate comprising a lowerelectrode; etching the heating material layer to form a heating layercomprising a first heating layer and a second heating layer; forming aninsulation layer on the top and side surfaces of the heating layer andon the top surface of the lower electrode; forming a contact hole in theinsulation layer so that a portion of the heating layer is exposed;forming a phase-change material layer filling the contact hole; andforming an upper electrode on the phase-change material layer.
 11. Themethod of claim 10, wherein the first heating layer comprises a materialhaving lower resistivity than the resistivity of a material forming thesecond heating layer.
 12. The method of claim 11, wherein the firstheating layer comprises titanium nitride (TiN) and the second heatinglayer comprises polysilicon (poly Si) or polysilicon germanium(poly-SiGe).
 13. The method of claim 10, wherein the first heating layercomprises a material which blocks diffusion of titanium.
 14. The methodof claim 13, wherein the first heating layer comprises at least oneselected from the group consisting of TaN, TiAlN, WN, WBN, TiSiN, TaSiN,WSiN, TiSiC, TaSiC, WSiC, and low resistivity TiN.
 15. The method ofclaim 14, wherein the second heating layer comprises high resistivityTiN.
 16. The method of claim 14, wherein the low resistivity TiN hasresistivity of 100 μΩ·cm or less.
 17. The method of claim 10, whereinthe first heating layer comprises a material having higher resistivitythan the resistivity of a material forming the second heating layer andthe second heating layer comprises a material having lower thermalconductivity than the thermal conductivity of a material forming thefirst heating layer.
 18. The method of claim 17, wherein the firstheating layer comprises TiAlN and the second heating layer comprisesTaN, TiN, or polysilicon germanium (poly-SiGe).
 19. A method ofmanufacturing a Phase-change Random Access Memory (PRAM) devicecomprising: forming an insulation layer on a substrate comprising alower electrode; forming a contact hole in the insulation layer so thata portion of the lower electrode is exposed; forming a second heatinglayer in the contact hole; forming a first heating layer on the secondheating layer; and sequentially forming a phase-change material layerand an upper electrode on the first heating layer.
 20. The method ofclaim 19, wherein the first heating layer comprises a material havinglower resistivity than the resistivity of a material forming the secondheating layer.
 21. The method of claim 20, wherein the first heatinglayer comprises titanium nitride (TiN) and the second heating layercomprises polysilicon (poly Si) or polysilicon germanium (poly-SiGe).22. The method of claim 19, wherein the first heating layer comprises amaterial which blocks diffusion of titanium.
 23. The method of claim 22,wherein the first heating layer comprises at least one selected from thegroup consisting of TaN, TiAlN, WN, WBN, TiSiN, TaSiN, WSiN, TiSiC,TaSiC, WSiC, and low resistivity TiN.
 24. The method of claim 23,wherein the second heating layer comprises high resistivity TiN.
 25. Themethod of claim 23, wherein the low resistivity TiN has resistivity of100 μΩ·cm or less.